This invention relates to the metering and control of fluids, and more particularly relates to the metering and control of fluids of aircraft passenger supplemental oxygen, particularly as would be used in a commercial aircraft airliner.
Emergency oxygen supply systems, such as are typically installed on aircraft to supply oxygen to passengers upon loss of cabin pressure at altitudes above about 12,000 feet, typically include a source of supplemental breathable oxygen connected to a face mask that is released from an overhead storage compartment when needed. The flow of breathable oxygen should be sufficient to sustain passengers until cabin pressure is re-established, or until a lower, safer altitude can be reached.
Presently, in passenger oxygen systems of large aircraft utilizing a gaseous oxygen supply source, oxygen is typically distributed from a centrally located bank of storage vessels or cylinders by a network of piping to manifolds that are commonly located adjacent to each row of seats. Each passenger mask is typically supplied via a separate orifice of the manifold. By varying the input pressure to the manifolds, the flow of oxygen to each of the masks can be varied.
When the emergency oxygen is to be supplied to a face mask, a constant flow of oxygen is typically received by a reservoir bag attached to the face mask. The oxygen is commonly supplied continuously at a rate that is calculated to accommodate even the needs of a passenger with a significantly larger than average tidal volume who is breathing at a faster than average respiration rate. The continuing flow of oxygen into the reservoir bag and into the mask is typically diluted by cabin air.
Inefficiencies in aircraft emergency oxygen supply systems can require the emergency oxygen supply to be larger and heavier than necessary, which has an adverse impact on the payload capacity and fuel consumption of the aircraft. For example, one known aircraft emergency oxygen supply system delivers a fixed oxygen flow suitable for the maximum cabin altitude contemplated, regardless of the actual cabin altitude that prevails. While this is a safe approach, it results in high oxygen consumption that requires a large and heavy oxygen supply.
Enhancing the efficiency of such aircraft emergency oxygen supply systems either in terms of the generation, storage, distribution or consumption of oxygen could therefore yield a weight savings. Conversely, an enhancement of an aircraft emergency oxygen supply system's efficiency without a commensurate downsizing would impart a larger margin of safety in the system's operation. It is therefore highly desirable to enhance the efficiency of an emergency oxygen supply system in any way possible.
The delivered supplemental oxygen flow rate needed to properly oxygenate an aircraft cabin occupant depends on the prevailing pressure altitude. The quantity of oxygen delivered to a user can advantageously be varied as a function of altitude, so that the quantity delivered produces proper oxygenation, while avoiding an inefficient and wasteful delivery of a greater quantity of oxygen than is required.
While efficient delivery of oxygen to each cabin occupant at the minimum required flow rate for a given altitude is desirable, variations in oxygen delivery to various masks distributed about the cabin due to variations in the pressure drop between locations in the piping system can result in some oxygen masks receiving oxygen flow at a lower rate than the average rate of oxygen flow. Because the system design is required to ensure that even the least favored mask must receive a sufficient supply, it follows that more oxygen than the minimum amount required to suitably oxygenate the user of a mask can be delivered to a mask receiving an average oxygen flow. Delivery of an average excess oxygen to masks to compensate for pressure variations within the distribution system constitutes a second inefficiency in the delivery of oxygen.
One conventional response to the issue of altitude variations has been the use of a so-called “altitude compensating regulator.” In a typical altitude compensating regulator, an aneroid barometer adjusts the output pressure of the regulator in response to changes in pressure altitude within the cabin. However, altitude compensating regulators often deliver an optimum flow at one altitude range and greater-than-optimum flow at other altitudes, as a consequence of the operating principles and control laws that govern the performance of pneumatic oxygen regulators. Further, a centrally located altitude compensating regulator fails to address the differences in flow rates at various locations in the piping network that result from variations in pressure drops within different regions of the piping network.
A disadvantage of a conventional electronic altitude compensating regulator is that the controller must be capable of generating signals that can move the valve to a multiplicity of positions, adding to complexity and cost. The valve also must have features that render it capable of responding by adopting a multiplicity of positions. Furthermore, the use of a single electronic regulator does not address the issue of different flows being delivered at different locations in the aircraft due to the varied pressure drops in the distribution lines.
One conventional aircraft emergency oxygen supply system utilizes an electrically operated valve that is capable of assuming a multiplicity of states between fully open and fully closed. This approach allows the aircraft emergency oxygen supply system to operate more efficiently at a range of altitudes, but utilizes a valve that is complex in its principle of operation and its performance, and that is therefore expensive and difficult to design and manufacture.
Another conventional aircraft emergency oxygen supply system supplies passengers with a first fraction of air enriched in oxygen from high pressure oxygen cylinders during a descent phase of the aircraft between a normal cruising altitude and an intermediate rerouting altitude. Compressed air is taken from a source of compressed air in the aircraft to produce a second fraction of air enriched in oxygen delivered to passengers during a phase of stabilized flight of the aircraft greater than 5,500 meters.
Another conventional aircraft emergency oxygen supply system calculates oxygen required and monitors the oxygen supply and flight level after emergency cabin decompression. The system utilizes a pressurized oxygen supply which feeds oxygen into the interior of the plane when it flies at high cabin altitudes, and the system indicates the changing status of the supply as oxygen is drained from the system. The system includes a pressure transducer coupled to the supply, and determines the rate at which the pressure of the supply is reduced, to yield a first signal representing this pressure lapse rate, and to concurrently determine the lapse rate at which the number of liters of oxygen in the supply is reduced, to yield a second signal representing the liter lapse rate. When oxygen is being drained from the supply, the system calculates the prevailing supply pressure, the number of liters remaining in the supply, and the time in hours and minutes remaining before the supply is exhausted, based on the current rate of oxygen consumption.
Another known aircraft emergency oxygen supply system includes pressurized oxygen storage for feeding a pipe with pressurized oxygen, and a distribution unit that responds to loss of pressurization at high altitude. The distribution unit delivers pressurized oxygen at a pressure that increases up to a first value that is reached when loss of pressurization occurs under an altitude of about 40,000 feet, and delivers pressurized oxygen at a pressure at a second value of about two times the first value, at an altitude above about 40,000 feet.
It would be desirable to provide an aircraft emergency oxygen supply system utilizing a simple electrically operated valve having on and off positions in combination with one or more suitable pressure transducers and suitable control logic to supply oxygen in a manner that is adjusted in response to the prevailing cabin altitude, to ensure that sufficient supplemental oxygen is dispensed for the particular cabin altitude condition that prevails, without dispensing more oxygen than is needed under the altitude condition, and to minimize the weight of the associated oxygen supply. It would also be desirable to provide an aircraft emergency oxygen supply system that efficiently uses multiple control zones within an aircraft, as well as multiple oxygen storage sources that are distributed through the aircraft. The present invention satisfies these and other needs.